You see this often in questions of users with Spanish as mother tongue. The
¿ has utterly no meaning in correct English. In my opinion it can always safely be auto-removed. This saves the editors from some extra effort.
I haven't ever seen the inverted exclamation mark
¡ being used, but perhaps this can be added to the blacklist as well.
Update: as being an avid SO user I did not immediately realize that meta.stackoverflow.com also covers meta.stackexchange.com; I'd like to clarify more that this request was intentionally targeted on stackoverflow.com alone, not really on other SE sites. I'm also not sure if this kind of features can be configured on a per-site level, but I'd imagine that this is possible.